917 research outputs found
Charged Rotating Kaluza-Klein Black Holes Generated by G2(2) Transformation
Applying the G_{2(2)} generating technique for minimal D=5 supergravity to
the Rasheed black hole solution, we present a new rotating charged Kaluza-Klein
black hole solution to the five-dimensional Einstein-Maxwell-Chern-Simons
equations. At infinity, our solution behaves as a four-dimensional flat
spacetime with a compact extra dimension and hence describes a Kaluza-Klein
black hole. In particlar, the extreme solution is non-supersymmetric, which is
contrast to a static case. Our solution has the limits to the asymptotically
flat charged rotating black hole solution and a new charged rotating black
string solution.Comment: 24 page
Topology Change of Coalescing Black Holes on Eguchi-Hanson Space
We construct multi-black hole solutions in the five-dimensional
Einstein-Maxwell theory with a positive cosmological constant on the
Eguchi-Hanson space, which is an asymptotically locally Euclidean space. The
solutions describe the physical process such that two black holes with the
topology of S^3 coalesce into a single black hole with the topology of the lens
space L(2;1)=S^3/Z_2. We discuss how the area of the single black hole after
the coalescence depends on the topology of the horizon.Comment: 10 pages, Some comments are added. to be published as a letter in
Classical and Quantum Gravit
Wiretapping a hidden network
We consider the problem of maximizing the probability of hitting a
strategically chosen hidden virtual network by placing a wiretap on a single
link of a communication network. This can be seen as a two-player win-lose
(zero-sum) game that we call the wiretap game. The value of this game is the
greatest probability that the wiretapper can secure for hitting the virtual
network. The value is shown to equal the reciprocal of the strength of the
underlying graph.
We efficiently compute a unique partition of the edges of the graph, called
the prime-partition, and find the set of pure strategies of the hider that are
best responses against every maxmin strategy of the wiretapper. Using these
special pure strategies of the hider, which we call
omni-connected-spanning-subgraphs, we define a partial order on the elements of
the prime-partition. From the partial order, we obtain a linear number of
simple two-variable inequalities that define the maxmin-polytope, and a
characterization of its extreme points.
Our definition of the partial order allows us to find all equilibrium
strategies of the wiretapper that minimize the number of pure best responses of
the hider. Among these strategies, we efficiently compute the unique strategy
that maximizes the least punishment that the hider incurs for playing a pure
strategy that is not a best response. Finally, we show that this unique
strategy is the nucleolus of the recently studied simple cooperative spanning
connectivity game
Kaluza-Klein Multi-Black Holes in Five-Dimensional Einstein-Maxwell Theory
We construct the Kaluza-Klein multi-black hole solutions on the
Gibbons-Hawking multi-instanton space in the five-dimensional Einstein-Maxwell
theory. We study geometric properties of the multi-black hole solutions. In
particular, unlike the Gibbons-Hawking multi-instanton solutions, each
nut-charge is able to take a different value due to the existence of black hole
on it. The spatial cross section of each horizon can be admitted to have the
topology of a different lens space L(n;1)=S^3/Z_n addition to S^3.Comment: 8 pages, to be published in Classical and Quantum Gravit
Spin diffusion/transport in -type GaAs quantum wells
The spin diffusion/transport in -type (001) GaAs quantum well at high
temperatures ( K) is studied by setting up and numerically solving the
kinetic spin Bloch equations together with the Poisson equation
self-consistently. All the scattering, especially the electron-electron Coulomb
scattering, is explicitly included and solved in the theory. This enables us to
study the system far away from the equilibrium, such as the hot-electron effect
induced by the external electric field parallel to the quantum well. We find
that the spin polarization/coherence oscillates along the transport direction
even when there is no external magnetic field. We show that when the scattering
is strong enough, electron spins with different momentums oscillate in the same
phase which leads to equal transversal spin injection length and ensemble
transversal injection length. It is also shown that the intrinsic scattering is
already strong enough for such a phenomena. The oscillation period is almost
independent on the external electric field which is in agreement with the
latest experiment in bulk system at very low temperature [Europhys. Lett. {\bf
75}, 597 (2006)]. The spin relaxation/dephasing along the diffusion/transport
can be well understood by the inhomogeneous broadening, which is caused by the
momentum-dependent diffusion and the spin-orbit coupling, and the scattering.
The scattering, temperature, quantum well width and external magnetic/electric
field dependence of the spin diffusion is studied in detail.Comment: 12 pages, 6 figures, to be published in J Appl. Phy
Charged Black Holes in a Rotating Gross-Perry-Sorkin Monopole Background
We present a new class of stationary charged black hole solutions to
five-dimensional Einstein-Maxwell-Chern-Simons theories. We construct the
solutions by utilizing so called the squashing transformation. At infinity, our
solutions behave as a four-dimensional flat spacetime plus a `circle' and hence
describe a Kaluza-Klein black hole. More precisely, our solutions can be viewed
as a charged rotating black hole in a rotating Gross-Perry-Sorkin monopole
background with the black hole rotation induced from the background rotation.Comment: 25 pages, 6 figure
Hole spin relaxation in [001] strained asymmetric Si/SiGe and Ge/SiGe quantum wells
Hole spin relaxation in [001] strained asymmetric Si/SiGe
(Ge/SiGe) quantum wells is investigated in the situation with
only the lowest hole subband being relevant. The effective Hamiltonian of the
lowest hole subband is obtained by the subband L\"owdin perturbation method in
the framework of the six-band Luttinger model, with
sufficient basis functions included. The lowest hole subband in Si/SiGe quantum
wells is light-hole like with the Rashba spin-orbit coupling term depending on
momentum both linearly and cubically, while that in Ge/SiGe quantum wells is a
heavy hole state with the Rashba spin-orbit coupling term depending on momentum
only cubically. The hole spin relaxation is investigated by means of the fully
microscopic kinetic spin Bloch equation approach, with all the relevant
scatterings considered. It is found that the hole-phonon scattering is very
weak, which makes the hole-hole Coulomb scattering become very important. The
hole system in Si/SiGe quantum wells is generally in the strong scattering
limit, while that in Ge/SiGe quantum wells can be in either the strong or the
weak scattering limit. The Coulomb scattering leads to a peak in both the
temperature and hole density dependences of spin relaxation time in Si/SiGe
quantum wells, located around the crossover between the degenerate and
nondegenerate regimes. Nevertheless, the Coulomb scattering leads to not only a
peak but also a valley in the temperature dependence of spin relaxation time in
Ge/SiGe quantum wells.... (The remaining is omitted due to the limit of space).Comment: 12 pages, 11 figures, PRB in pres
Schwarzschild black hole levitating in the hyperextreme Kerr field
The equilibrium configurations between a Schwarzschild black hole and a
hyperextreme Kerr object are shown to be described by a three-parameter
subfamily of the extended double-Kerr solution. For this subfamily, its Ernst
potential and corresponding metric functions, we provide a physical
representation which employs as arbitrary parameters the individual Komar
masses and relative coordinate distance between the sources. The calculation of
horizon's local angular velocity induced in the Schwarzschild black hole by the
Kerr constituent yields a simple expression inversely proportional to the
square of the distance parameter.Comment: 6 pages, 1 figure; improved versio
Report on workshop A1: Exact solutions and their interpretation
I report on the communications and posters presented on exact solutions and
their interpretation at the GRG18 Conference, Sydney.Comment: 9 pages, no figures. Many typos corrected. Report submitted to the
Proceedings of GR18. To appear in CQ
Sequences of dipole black rings and Kaluza-Klein bubbles
We construct new exact solutions to 5D Einstein-Maxwell equations describing
sequences of Kaluza-Klein bubbles and dipole black rings. The solutions are
generated by 2-soliton transformations from vacuum black ring - bubble
sequences. The properties of the solutions are investigated. We also derive the
Smarr-like relations and the mass and tension first laws in the general case
for such configurations of Kaluza-Klein bubbles and dipole black rings. The
novel moment is the appearance of the magnetic flux in the Smarr-like relations
and the first laws.Comment: 26 pages, 1 figur
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